This may explain why you had a problem: click here
As you say, I think that it is best to wait until Windows Update makes it available to you.
IMHO, the most important tip is to shut down all programs before installing the service pack, especially antivirus and firewall. I have Kaspersky Internet Security (KIS) and WinPatrol running. I left them running while I downloaded the update (through Windows Update) and then closed them before installing. After rebooting, KIS came up with a number of popups saying programs/files had been changed. I allowed all of these and everything seems to be working well.